1. Field of Invention
This invention relates generally to pumps for liquids, and more particularly, to centrifugal pump cutters for cutting solids suspended in the liquid.
2. Description of Related Art
Pumps in both the manure slurry and municipal waste markets are subject to clogging due to the nature of stringy materials and other soft solids which tend to restrict or block the impeller passages in a centrifugal pump. This clogging can occur as often as every few days.
One attempt to solve the clogging problem was provided by a drawing of an “A Series Cutter Assembly: Drawing #046897” to Homa. The Homa assembly is a crude welded device with a single slicer blade welded to a cutter plate, and two flat slicer blades welded inside an impeller and leaving a small opening therebetween. The Homa assembly has operational flaws, including shortcomings present in any welded device designed without thought to hydraulic impact of the cutters. For example, the Homa cutter and stator teeth block flow into the impeller, causing substantial pressure drop as flow enters the pump. This pressure drop will limit the amount of “lift” that the pumps can generate, limit the flow range of a pump, limit the size of a solid that can flow through the pump, and increase the amount of power that would be required to operate the pump. With just one impeller tooth the cutting force is skewed to one side causing life reducing unbalanced loads. The cutter teeth and impeller will have a reduced operational life because of the unbalance.
The Homa mechanism is fabricated with the teeth welded into the impeller and stator. Welding the teeth adds problem on operation of the pump. For example, welds can be attacked by corrosion causing premature failure. Heating from the welds can damage the impeller and stator. That is, the heat could warp the teeth and change the base structure of the underlying material. The corrosion resistance near the weld can change because of the heat. In addition, impact loads (from cutting) are concentrated at the weld points leading to reduced impeller/stator life. Further, the welded on teeth are non-replaceable. This means that failure at the weld would likely require a new impeller or plate in order to make a repair that now requires a pump rebuild. Even prior to failure, the welded-on teeth are wear items and will need to be renewed on a regular basis. Since pumps can go several years without a major rebuild, the requirement that base parts (impeller/stator) be replaced with the teeth is an expensive time consuming problem for pump users.
All references cited herein are incorporated herein by reference in their entireties.